A friar is a Catholic man who belongs to a religious order and, in the past especially, lived very poorly and travelled about teaching Christianity, rather than staying shut away. Famous groups include Franciscans and Dominicans. English often contrasts friars with monks: a monk’s home is a monastery, and the tidy school picture is that he stays there; a friar’s calling was to go among people. Though actually, real history is messier — some monks left the house, some friars settled — but the old difference still shapes how the words are taught. Today you may still meet friars, though the wandering-poor picture belongs more to history and to stories. The word feels slightly old or church-bookish in everyday talk. It is not a general word for any priest.